U.S. Pat. No. 4,805,504 discloses a quick actuating mechanism for the movable guard of a power miter saw which at two ends of an actuating link has cam grooves. However the cam grooves are difficult to manufacture and the curvature is difficult to control. EP-A-0407204 discloses an arcuate slide slot mechanism and the guiding member which causes the sliding movement of the movable guard is fixed on the safety guard so that it is complex to assemble and inconveniently adjustable whilst demanding highly precise mounting. U.S. Pat. No. 5,203,245 discloses an assembly which comprises a slide slot in an actuating link and a link control bearing in a fixed guard. This construction is difficult to manufacture and has a complex slide slot.